1. Field of the Invention
The present invention relates to inorganic granules comprising inorganic compounds such as calcium phosphates, metal oxides and mixtures thereof or the like, and to a process for production thereof. The inorganic granules are useful as fillers for bony defects or as carriers for immobilized enzymes or catalysts.
2. Description of the Prior Art
Calcium phosphate granules, which are representative of inorganic granules, promote formation of new bone and integrate with the living bone tissue. Their use as bone fillers has thus been attempted.
As processes for production of calcium phosphate granules, there are known (a) a process which comprises grinding the dry product of calcium phosphates prepared by the wet process into granules, as is or after precalcination, and then sifting the granules (Journal of American Chemical Society, 89, 5535 (1967), Published Unexamined Japanese Patent Application No. 20558/86, etc.), (b) a process which comprises repeatedly stirring calcium phosphate powders with a high speed stirring machine in the presence of alcohol as a medium while moisturizing, to form granules of a desired size (Published Unexamined Japanese Patent Application No. 45748/86), etc. The calcium phosphate granules obtained by the processes as described above have uneven shapes in respective granules so that, in the case of using them as bone fillers, problems often occur in that the filling state is not uniform and they do not exhibit stable efficiency. In addition, the calcium phosphate granules obtained by the process (a) described above have edges that agitate bone cells and there is thus a fear of causing necrosis of the cells, in the case of filling them in a bony defect. Further, the calcium phosphate granules obtained by the process (b) described above give high density granules only with difficulty, even after calcination, and there is also a problem that mechanical strength thereof is poor for their use as bone fillers.
Furthermore, if granules of a desired size are sought to be made by these processes, there is a problem that yield is poor due to production of undesired powders in large quantities in either of the processes (a) and (b).